Low-Density Oil-Based Wellbore Fluid for Sag-Stable Drilling
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Solution Overview
Problem
Conventional drilling fluids used in rotary drilling have densities that are too high for depleted reservoirs, leading to issues such as sag and increased risk of fluid loss, particularly at lower temperatures, which can result in formation fluid influx and well damage.
Innovation Solution
Incorporation of rheology modifiers, such as polycarboxylic acids and polyamides, along with low density materials like hollow microspheres, to maintain fluid stability and suspend particles, achieving a specific gravity less than 0.83 and minimal sag over extended periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional drilling fluids with high density are used, then sufficient hydrostatic pressure is provided to prevent formation fluid influx, but the fluid density becomes too high for depleted reservoirs causing sag and increased risk of fluid loss
Solution Approach 1:
The patent applies parameter changes by modifying the density parameter of drilling fluid from conventional high density (greater than 8.3 ppg) to low density (less than 7.0 ppg, specifically 6.1-6.8 ppg). This is achieved by using a water-soluble polymer as viscosity modifier instead of traditional weighting materials, fundamentally changing the density parameter to suit depleted reservoir conditions while maintaining adequate hydrostatic pressure through optimized viscosity characteristics.
Solution Approach 2:
The patent applies local quality by tailoring the fluid properties specifically for depleted reservoir conditions. The drilling fluid formulation with specific gravity less than 0.83 and controlled viscosity characteristics is locally optimized for low-pressure reservoirs, allowing the fluid to maintain stability and prevent sag in this specific application context without being overly dense for other reservoir types.
2Quantity of substance
If fluid density is reduced for depleted reservoirs, then sag is minimized and fluid loss risk is reduced, but hydrostatic pressure may become insufficient to control subsurface pressures
Solution Approach 1:
The patent changes the pressure control mechanism from relying primarily on high density to utilizing optimized viscosity parameters. By using water-soluble polymers to achieve plastic viscosity of 20-40 cP and Fann 35 dial readings of 3-7 at 3 rpm, the fluid maintains adequate hydrostatic pressure and well control capability through rheological properties rather than excessive density, enabling low density (less than 7.0 ppg) operation in depleted reservoirs.
Solution Approach 2:
The patent substitutes the mechanical pressure control mechanism (high density providing hydrostatic pressure) with a rheological control mechanism (polymer-based viscosity modification). Instead of using heavy weighting materials to generate hydrostatic pressure, the system uses water-soluble polymers to create appropriate flow resistance and suspension capability, effectively replacing density-based pressure control with viscosity-based control suitable for low-pressure reservoirs.
3Stability of the object's composition
If rheology modifiers are added to maintain fluid stability, then particle suspension is improved and sag is reduced, but viscosity may increase excessively leading to lost circulation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the viscosity parameters within optimal ranges. The water-soluble polymer is formulated to achieve plastic viscosity of 20-40 cP and Fann 35 dial readings of 3-7 at 3 rpm, avoiding excessive viscosity. This optimized parameter range maintains adequate particle suspension and fluid stability while preventing viscosity-related lost circulation problems in depleted reservoirs.
Solution Approach 2:
The patent uses water-soluble polymers that can be easily adjusted and are biodegradable, replacing complex, long-lasting viscosity modifiers. These polymers provide temporary but sufficient viscosity enhancement during drilling operations, then dissolve or degrade, avoiding long-term viscosity buildup that could cause lost circulation. The approach uses simple, adjustable rheology modifiers rather than complex, persistent viscosity-enhancing materials.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively maintains fluid density and stability, reducing sag and preventing formation fluid influx, while avoiding excessive viscosity that could lead to lost circulation, even at low temperatures.
Implementation Method 1
an emulsifier stabilizing the non-oleaginous phase within the oleaginous phase
Implementation Method 2
at least one rheology modifier selected to suspend the low density material within the wellbore fluid
Data Source
AI summary
A wellbore fluid may include an oleaginous continuous phase; a non-oleaginous discontinuous phase; an emulsifier stabilizing the non-oleaginous phase within the oleaginous phase; a low density material selected and in an amount to result in a specific gravity of the wellbore fluid that is less than 0.83; and at least one rheology modifier selected to suspend the low density material within the wellbore fluid.